1. Field of the Invention
The present invention relates to a technique for handling wafers, including, for example, semiconductor wafers.
2. Description of the Prior Art
The handling of semiconductor wafers has been accomplished by a variety of techniques. For picking up a wafer, a vacuum-assisted handler has been used, wherein the wafer is pulled against a vacuum outlet. However, this results in the wafer being contacted by the handler, which can result in damage to the wafer. Hence, vacuum handlers are typically used only for picking up the wafer by its back side, which is the side opposite that on which the integrated circuits (or other devices) are formed. For picking up a wafer from the front side, it is known to use the Bernoulli effect, wherein a pressurized fluid is directed onto a surface of the wafer, creating a lateral flow across the surface. This produces a low pressure area that holds the wafer near the handler. However, the wafer is still free to move laterally, which may be prevented by the use of projections on the handler that surround the wafer. It is also known to use the Bernoulli effect to pick up a wafer, and then apply a vacuum while interrupting the Bernoulli air flow, in order to hold the wafer against the handler; see, for example, U.S. Pat. No. 4,566,726.
However, there are applications for a wafer handler that can not only pick up a wafer from its front side, but also load two wafers back-to-back in a boat for introduction into a furnace, or other processing apparatus. In that case, the wafer handler should be thin enough to fit into a boat having wafers in adjacent slots while not contacting those wafers. To facilitate loading and unloading boats or cassettes having bottoms and sides, it is also desirable that the handler cover less than half of the wafer. It is further desirable to be able to pick up a semiconductor wafer regardless of the location of the major or minor "flats", which are straight portions along the otherwise circular periphery of the wafer.